THE first edition of this volume of the Course of Theoretical Physics was publishedin two parts (1971 and 1974) under the title“Relativistic Quantum Theory”. Itcontained not only the basic material on quantum electrodynamics but also chap-ters on weak interactions and certain topics in the theory of strong interactions.The inclusion of those chapters now seems to us inopportune.The theory of strongand weak interactions is undergoing a vigorous development founded on newphysical ideas, and the situation in this field is changing very rapidly, so that thetime for a consistent exposition of the theory has not yet arrived. In the presentedition,therefore,we have retained only quantum electrodynamics，and accord-ingly changed the title of the volume.
As well as a considerable number of corrections and minor changes, we havemade in this edition several more significant additions，including the operatormethod of calculating the bremsstrahlung cross-section,the calculation of theprobabilities of photon-induced pair production and photon decay in a magneticfield,the asympiotic form of the scattering amplitudes at high energies，inelasticscattering of electrons by hadrons，and the transformation of electron-positronpairs into hadrons.
A word regarding notation. We have reverted to the use of circumflexed lettersfor operators, in line with the other volumes in the Course. No special notation isused for the product of a 4-vector and a matrix vector y”, previously denoted by acircumflexed letter; such products are now shown explicitly.
we have, alas, had to prepare this edition without the aid of Vladimir Berestets-ki, who died in 1977; but some of the added material mentioned above had beenput together previously, by the three authors jointly.
Our sincere thanks are offered to all readers who have given us their commentson the first edition of the book, and in particular to J. S. Bell, V: P.Krainov,L. B.Okun’, V. I. Ritus,M. I. Ryazanov and 1.S. Shapiro.